This application proposes a mixed method, ethno-epidemiological study of MSM Poz Parties in NYC. Poz Parties are an emerging type of sexual risk environment that are being replicated throughout the US and explicitly scripted for unrestricted sexual exchanges between HIV+ MSM. Specific aims of the proposed study include the following: 1. To describe MSM Poz Parties, including characteristics of the physical settings, participants, and social interactions, that collectively define this emerging MSM risk environment; 2. To describe the complex personal and social meanings that HIV+ MSM attach to sexual interactions in these environments, notably interactions that are explicitly scripted for sex without condoms and/or sex with multiple concurrent partners; 3. To describe the use of drugs within this environment, and the role that Poz Parties may have in facilitating exposure to, and initiation of, new types of drug and sexual interactions among HIV+ MSM; 4. To examine HIV+ MSM's rationales and motivations for participating in Poz Parties, and to compare sexual exchanges at Poz Parties with those outside Poz parties, with an interest in exploring sero-sorting and sero-disclosure dynamics. Both structured survey and ethnographic methodologies will be used: Structured screener survey will be conducted among 400 subjects attending one of an estimated 30 Poz Party events over the two years of data collection, with an additional 800 interviews among subjects attending multiple events. Screener surveys will be used to select subjects for a series of subsequent ethnographic interviews (N=75) that will be the source of intensive narrative data about 5 thematic domains, including Life History, Drug Initiation Practices, Sex Party Initiation/Practices, Unprotected Sex (Barebacking), and Dynamics of Sero-Status Disclosure in Non Poz Party sexual encounters. The study will inform our understanding of the sexual practices of HIV+ MSM, including sex with HIV- or serostatus unknown partners, risk for STD's, initiation of new drug and sexual practices, and HIV superinfection.